Device for heaving in, letting out and storing a chain

ABSTRACT

The device comprises a main windlass driving a main wildcat engaged with the chain. At least one chain locker located near the main wildcat receives the heaved-in wildcat portion. The main chain is located beyond the chain locker with respect to the direction in which the chain is heaved in by the main wildcat. An auxiliary wildcat disposed above the locker engages an intermediate section of the chain which extends between the main wildcat and the locker and a torque motor is drivingly connected to the auxiliary wildcat to impart to the intermediate chain section a constant tension irrespective of the direction of rotation of the main wildcat.

i United States Patent Ayme Nov. 4, 1975 DEVICE FOR HEAVING IN, LETTING OUT 3,243,090 3/1966 Shibata 254/1755 AND STORING A CHAIN 3,300,187 1/1967 Saxe et a1. 254/l75.7 3,750,970 8/1973 Tremoulet, Jr. 254/1755 [76] Inventor: Gerard Ayme, 5, rue Henri Guichard, 44,000 Nantes, France Filed: Dec. 6, 1973 Appl. No.: 422,140

US. Cl. 254/175.5; 114/235 R Int. Cl. B66D l/76 Field of Search 254/175.5, 175.7, 168, 254/167, 172; 226/77, 80, 86, 181; 114/235 R; 242/153, 154, 155 R, 82

[56] References Cited UNITED STATES PATENTS 2/1912 Froger 114/235 R 6/1942 Smith 254/175.5 2/1957 Jareckie 114/235 R 11/1958 Robins et a1 254/1755 Primary Examiner-Frank E. Werner Assistant ExaminerKenneth Noland Attorney, Agent, or Firml-1olman & Stern [57] ABSTRACT The device comprises a main Windlass driving a main wildcat engaged with the chain. At least one chain locker located near the main wildcat receives the heaved-in wildcat portion. The main chain is located beyond the chain locker with respect to the direction in which the chain is heaved in by the main wildcat. An auxiliary wildcat disposed above the locker engages an intermediate section of the chain which extends between the main wildcat and the locker and a torque motor is drivingly connected to the auxiliary wildcat to impart to the intermediate chain section a constant tension irrespective of the direction of rotation of the main wildcat.

13 Claims, 13 Drawing Figures U.S. Patent Nov. 4, 1975 Sheet 1 of4 3,917,229

US. Patent NOV.4, 1975 Sheet2of4 3,917,229

US. Patent Nov. 4, 1975 Sheet 3 of4 3,917,229

U.S. Patent Nov.4, 1975 Sheet4of4 3,917,229

DEVICE FOR HEAVING IN, LETTING OUT AND STORING A CHAIN The present invention relates to windlasses and wildcats for winding up a chain and storing the latter in a chain locker in particular on board certain vessels. More precisely, it concerns an improved device for pulling on the chain with a large force notwithstanding a hanging length which is too short to enable the weight of the chain to produce sufficient grip on the wildcat or notwithstanding a winding angle which is insufficient to ensure a good engagement with the wildcat. The invention also concerns the storage of the chain in an encumbered space. In particular, this device may be mounted on a tug boat or an auxiliary ship provided for raising and storing an anchor and its chain which is fixed at the end thereof opposed to the ship (directly or through a cable) to for example a drilling platform out at sea.

Putting in the chain by means ofa winch requires laying and spreading it in the form ofa concertina and this takes up space and is hardly a practical operation. Winding the chain onto a drum implies an unshackling of the chain and a time-consuming operation.

If a wildcat of conventional type having a horizontal axis is employed (on a winch shaft or in an independent manner), the chain N must be stored just below this wildcat B of the ship R, as shown in FIG. 2 of the accompanying drawings. Now, it is known that ships of this type have little available space on board. The locker P for the chain is often located in the vicinity of the engine room. Badly positioned, the locker is necessarily shallow. Often, the calibre of the chain is such that the chain locker located under the wildcat B is very rapidly obstructed so that no counterweight portion of the chain can compensate for C for the small winding angle A on the wildcat B, whereas a large pull is usually required for winding up the chain N.

FIG. la shows, for example, that if the chain storage capacity on the tug boat R is thus limited, the major part of the chain N can only be stored on board the ship that the tug boat is intended to draw along, as the illustrated platform PL. But this results in respect of long lengths of chain in the latter being dragged along the bottom of the sea in the three following cases:

when winding up (or raising) the chain; this operation then requires a high powered windlass G on the platform PL (FIG. I);

when casting the anchor and the chain from the platform PL with the aid of the tug boat R; it is then the pulling power of the latter which must be very high.

Sometimes, the platform PL is anchored through a cable and an anchor with an intermediate chain. To raise the anchor, it is not easy to pull on board the platform PL the chain after the cable. The tug boat R must then take on board all of the chain when raising the anchor (FIG. la). Likewise, it must cast all of the chain off when dropping the anchor.

It is clear from the foregoing that it is of interest to be able to wind in and then store rapidly and easily the largest possible amount of chain on board the tub boat R.

An object of the present invention is to overcome these drawbacks.

The invention provides a device for heaving in, letting out and storing a chain, in particular on board a vessel such as a ship or a floating platform, comprising a main windlass provided with at least one main wildcat or sprocket wheel engaging said chain so as to effect the heaving in and the letting out of the chain, and at least one chain locker placed near to the main wildcat for receiving the portion of chain heaved in, wherein the main wildcat is placed beyond said chain locker with respect to the direction in which the useful section of the wildcat or sprocket wheel extends, and an auxiliary chain is disposed above the chain locker and engages an intermediate section of chain which extends between the main wildcat and the chain locker, a torque motor being provided for imparting to said intermediate chain section a constant tension irrespective of the direction of rotation of the main wildcat.

With this feature, it is possible to achieve a marked increase in the angle of winding or overlap of the chain on the main wildcat. This angle may exceed if desired. Consequently, the pulling force of the main wildcat no longer depends on the length of chain hanging in the chain locker. The latter may therefore be shallow if necessary.

According to another feature of the invention, there are provided a plurality of aligned chain lockers each of which has its own auxiliary wildcat driven by a separate torque motor, these chain lockers being adapted to receive in succession a part of said chain by successive engagement with the associated wildcat.

It is thus possible to distribute the chain over a plurality of lockers and thus totally clear the deck of the vessel, the lockers having if desired a depth which is a function solely of the space available on board the vessel in the region in which lockers are provided.

Further features and advantages of the invention will be apparent from the ensuing description with reference to the accompanying drawings.

In the drawings:

FIG. 1 is a view of a tug boat which is heaving in the anchoring chain of a floating platform;

FIG. la is a similar view, but to an enlarged scale, of the tug boat with a cable and chain;

FIG. 2 is a diagrammatic view of a conventional chain windlass with its chain locker;

FIG. 3 is a perspective view of a device according to the invention comprising a main windlass and an auxiliary wildcat which improves the engagement of the chain on the main wildcat;

FIGS. 4 and 5 are elevatio'nal views, partly in section, of a device according to the invention comprising a main windlass and three auxiliary wildcats above three chain lockers (FIG. 4 corresponding to the start of the storage and FIG. 5 to an intermediate period of the storage);

FIG. 6 is a view similar to FIGS. 4 and 5 in which there is employed a single auxiliary wildcat which is movable over the chain lockers;

FIG. 7 is a plan view of the deck of a vessel having two wildcat embarking systems with a mobile auxiliary chain (three lockers on each side of the vessel), the main and auxiliary wildcats having horizontal axes;

FIG. 8 is an elevational view of a device having a main windlass having a vertical axis and three auxiliary wildcats at fixed stations and having horizontal axes, these wildcats being oriented in different ways above their lockers;

FIG. 9 is a plan view of the device shown in FIG. 8;

FIG. 10 is a longitudinal sectional view of a locker having a device according to the invention with a main wildcat having a vertical axis and auxiliary Wildcats having vertical, axes and disposed at fixed stations;

FIG. 11 is a plan view of the device shown in FIG. 10,

and

FIG. 12 is a longitudinal diagrammatic view of the stern of a drill ship and a chain heaving device according to the invention.

The chain winding and storing device according to the invention comprises in a first embodiment (FIG. 3) a main Windlass 1 with its wildcat or sprocket wheel 2 which engages with a chain 3 whose portion 4 located downstream of the wildcat 2, with respect to the direction of chain winding, is held taut by an auxiliary windlass 5. The latter is located above a chain locker 6 which opens onto the deck 7 ofa ship for example. The auxiliary pull exerted on the portion 4 is effected always in the same direction indicated by arrow F irrespective of the direction of rotation of the wildcat 2 (heaving in or letting out the chain 3). The value of the auxiliary pull exerted by the wildcat or sprocket wheel 8 (here having by way of example six cogs although this number may be four or more) of the auxiliary Windlass is very low with respect to the forces exerted through the main wildcat on the chain portion 3. It is substantially constant irrespective of the direction of displacement of the chain portion 3. The purpose thereof is to tension the portion 4 and cause the chain to wind round or overlap the wildcat 2 with a large angle which improves the engagement. The chain then descends by the effect of its own weight at 9 and fills the chain locker 6 until the upper end of the latter is reached, if necessary. The auxiliary pull therefore compensates for the lack of weight of the portion 9 which hangs from the wildcat 8 in the shallow chain locker. It isproduced by a motor which is constantly carrying current or under pressure according as it is an electric or hydrau lic motor. It may be, for example, a torque motor of known type which, irrespective of the direction of rotation of the wildcat 8 (driven by the chain), exerts on the wildcat 8 a low torque in the direction of arrow G. In other words, the direction of application of the torque exerted by the torque motor remains the same (direction G) whether the winding be produced when dropping the anchor (letting out the chain) or when raising the anchor (heaving in the chain). The overall size of the Windlass 5 is small since its power is low.

FIGS. 4 and 5 show the chain 3 which is heaved in by a main Windlass 1 withits wildcat 2, then passes in succession over the auxiliary Wildcats or sprocket wheels 10, 11, 12 provided with their respective torque motors. The portions l3, l4, 15 of the chain are held taut at the start of the operation. As soon as the most remote chain locker 16 has been filled (FIG. 5), the torque motor of the wildcat 12 is stopped. The chain then engages naturally in the following chain locker 17, the portions 13 and 14 remaining taut. When the locker 17 is filled, the wildcat 11 is stopped and the locker 18 is filled, the portion 13 alone then being taut. The storage capacity is therefore greater, the number of lockers and auxiliary Wildcats being chosen as desired. The position of these elements is chosen invaccordance with requirements on board, in particular in accordance with the position of the engine room below the deck.

By way ofa modification (FIGS. 6 and 7), the auxiliary wildcat 19 is single and mounted on a carriage 20 which travels along rails 21 through rollers 22. The carriage 20 may be moved in an independent manner by a remote-controlled motor 23. As many stopping positions 19, 19a and 191; (which may be automatic) as chain lockers 24, 25, 26, enable the latter to be filled in succession.- An optional locking system 27 enables the carriage to be fixed above each one of the chain lockers. The chain portion 28 always remains taut owing to the effect of the torque motor. The operation may be rendered automatic if desired. There may be any number of lockers. A plurality of chain storing systems, one on each side of the vessel for example, may be arranged on the deck in a symmetrical or asymmetrical manner. FIG. 7 shows that each main wildcat 2 is mounted at the end of a drum whereby other cables or chains may be wound.

In FIGS. 8-11, the main wildcat or sprocket wheel 29 may have a vertical axis of rotation. It is driven by a I Windlass or other device located above or below the deck of the ship depending on the space left free by the engine room 30 containing the machinery propelling the ship. It is placed in accordance with other winches 31 (for example for raising the anchor) disposed on the deck for other purposes. Preferably, it is mounted on the axis of the ship so as to be capable of storing the chain in the chain lockers located on the port side (32, 33, 34) and the starboard side. (35, 36, 37).

The auxiliary wildcats38, 39, 40 with their torque motors may have a horizontal axis of rotation and be at fixed stations (FIGS. 8 and 9). The angle in plan of the. vertical plan of the face of each wildcat is then a function of its distance from the main wildcat so as to precIude a jumping of the chain from the Wildcats. It will be clear that in this case it is necessary to cause the chain to jump or disengage from the wildcat40 when the locker 37 is full and then to pass the wildcat round the chain 39 so as to fill the locker 36 and so on until all the lockers are occupied by the chain. To change, the side of the ship it is necessary to reverse the winding of the chain on the main wildcat 29. According to another modification, the auxiliary wildcats 41, 42, 43 have a vertical axis of rotation (FIGS. 10 and 11). It is then possible to fill the corresponding lockers 46, 47, 48 in succession according to the previously-described method illustrated in FIGS.-4 and 5, on condition that the portion 44 is held taut by a force exerted by the torque motor of each auxiliary wildcat in the direction of arrows H. If it is desired to obtain an improved wind ing angle on the wildcat 29, the chain portion 45 may also be put under tension by the torque motor which exerts its torque in the direction of arrow J. After stoppage of the torque motor of the wildcat 43 (locker 46 filled), the chain is passed manually onto the wildcat 42. Normally, the chain must then fill the locker 47 and then the locker 48. It will be understood that the same is true in respect of the row of lockers on the port side of the ship after having changedthe direction of windingof the chain on the main Wildcat 29.

According to another modification, the Wildcats 38, 39, 40 (FIGS. 8 and 9) may be replaced by a single.

wildcat having a horizontal axis of rotation and travelling above the chain lockers. The auxiliary Windlass assembly (wildcat and torque motor) is then mounted on a turret T (see the lower part of FIG. 9) which is mounted on a carriage to pivot about a vertical axis fixed relative to the carriage so as to be capable of suitably orienting the plane of engagement of the wildcat. This orientation is then variable for each one of the positions above the corresponding locker. It can be automatic or'manual with preferably possibility of locking the position. This arrangement is derived directly from the embodiment described hereinbefore with reference to FIG. 6. In particular, the rails 21, the rollers 22and the carriage 20 are identical, the latter being however provided with the turret T:

According to another modification, the wildcats having vertical axes of rotation, .41, 42, 43 (FIGS. and 11) are also replaced-by a single wildcat having a vertical axis of rotation which is also mounted on a carriage (but without a turret) travelling above the chain locker.

The device according to the invention may be mounted on any vessel on which chains .are to be embarked and in which chain. storage poses a problem owing to lack of space. Thus, the tug boats or auxiliary ships (supply ships) serving drilling platform's may be equipped with the device.

The device according to the invention is also applicable (FIG. 12) to drill ships which move with their drilling equipment (derrick) 49, the ships being required to embark chains 50 which have a large overall size in one or a plurality of shallow chain lockers 51. The angle a of winding or overlap may be increased so as to improve the engagement of the chain on the main wildcat 5 by means of an auxiliary wildcat 53 with its torque motor.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is 1. A device for heaving in, letting out and storing a chain, in particular on board a vessel such as a ship or a floating platform, comprising a main windlass provided with at least one main wildcat for engagement with the chain for heaving in and letting out the chain and connected to be driven by the windlass, and at least one chain locker located near the main wildcat for re-' ceiving a heaved-in chain portion, the main wildcat being placed beyond said chain locker with respect to the direction in which the chain is heaved in by the main wildcat, an auxiliary wildcat disposed above the chain locker for engagement with an intermediate section of the chain which intermediate section extends between the main wildcat and the chain locker, and a torque motor drivingly connected to the auxiliary wildcat for imparting to said intermediate chain section a constant tension irrespective of the direction of rotation of the main wildcat.

2. A device as claimed in claim 1, comprising a plurality of aligned chain lockers, a plurality of wildcats,

each of which is located above a respective one of said,

plurality of chain lockers and drivingly connected to a corresponding torque motor for driving said auxiliary wildcat, the chain lockers being adapted to receive in succession a portion of said chain by the successive engagement of the chain with the associated auxiliary wildcat.

3. A device as claimed in claim 2, wherein the main wildcat and the auxiliary wildcat have horizontal axes of rotation and are contained in the same vertical plane.

4. A device as claimed in claim 2, comprising two main wildcats both driven by said main windlass, the aligned chain lockers being provided in two groups of chain lockers located respectively on the port side and starboard side of the vessel, the two main wildcats cooperating respectively with two auxiliary wildcats respectively pertaining to the two groups of chain lockers.

5. A device asclai'm'ed in claim-1,comprising a single main wildcathavinga vertical axis of'rota'tion, a plurality of aligned chain lockers, the aligned chain lockers being provided in two groups of aligned chain lockers located respectively on the port side and starboard side ofthe vessel/a separate auxiliary wildcat having a hori- "zontal axis ofrotation being provided above each chain 6. A device 'as claimed in claim 1, comprising a single main wildcat having a vertical axis of rotation, a plurality of'aligned chain lockers} the aligned chain lockers being provided in twog'r'oups of aligned chain lockers located respectively on the port side and starboard side of the vesseLand auxiliary wildcat's wh'ich have vertical axes o? rotation and are respectively'asso'ciated with the two groups of aligned chain lockers.

7 A device "for heavinginflet ting out and storing a chain, in particularon'boarda vessel such as a ship or a floating platform, comprising a main windlass provided with at least one main wildcat for engagement with the chain for heaving in and letting out the chain and connected to be driven by the windlass, a plurality of aligned chain lockers for receiving in succession heaved-in portions of said chain, the main wildcat being placed beyond said chain lockers with respect to the direction in which the chain is heaved in by the main wildcat, an auxiliary wildcat, a torque motor drivingly connected to the auxiliary wildcat, support means for carrying the assembly of said torque motor and said auxiliary wildcat and means associated with said support means for allowing translational movement of said support means above the chain lockers for engagement of said auxiliary wildcat with an intermediate section of the chain, which intermediate section extends between the main wildcat and that one of the chain lockers which is being filled with a portion of said chain by the auxiliary wildcat, said torque motor and said auxiliary wildcat imparting to said intermediate chain section a constant tension irrespective of the direction of rotation of the main wildcat.

8. A device as claimed in claim 7, comprising two main wildcats both driven by said main windlass, the aligned chain lockers being provided in two groups of chain lockers located respectively on the port side and starboard side of the vessel, each main wildcat cooperating with a respective auxiliary wildcat, each auxiliary wildcat being drivingly connected to a torque motor whereby each auxiliary wildcat and each torque motor constitute an assembly mounted on a support means associated with a means allowing translational movement of said assembly above the respective group of aligned chain lockers.

9. A device as claimed in claim 7, comprising a single main wildcat having a vertical axis of rotation, the aligned chain lockers being provided in two groups of aligned chain lockers located respectively on the port side and starboard side of the vessel, there being provided for each group of chain lockers an assembly of a torque motor and the corresponding auxiliary wildcat which has a horizontal axis of rotation, said assembly being mounted on a support means associated with means for allowing translational movement of said support means above the respective chain lockers, said assembly being pivotably mounted about a vertical axis on said support.

10. A device as claimed in claim 9, further comprising, for each of said assemblies, rails extending on each side of the respective groups of chain lockers, a carriage for rolling along the rails, and a turret pivotably mounted on said carriage for supporting the corresponding assembly of a torque motor and an auxiliary wildcat.

11. A device for heaving in, letting out and storing a chain, in particular on board a vessel such as a ship or a floating platform, comprising a main Windlass prO- vided with at least one main wildcat for engagement with the chain for heaving in and letting out the chain and connected to be driven by the windlass, a plurality of aligned chain lockers for receiving in succession heaved-in portions of said chain, the main wildcat being placed beyond said chain lockers with respect to the direction in which the chain is heaved in by the main wildcat, an auxiliary wildcat mounted to be movable in translation above the chain lockers for engagement with an intermediate section of the chain, which intermediate section extends between the main Wildcat and that one of the chain lockers which is being filled with a portion of said chain by the auxiliary wildcat,

and a torque motor drivingly connected to the auxiliary stationary in selected positions on the rails. 

1. A device for heaving in, letting out and storing a chain, in particular on board a vessel such as a ship or a floating platform, comprising a main windlass provided with at least one main wildcat for engagement with the chain for heaving in and letting out the chain and connected to be driven by the windlass, and at least one chain locker located near the main wildcat for receiving a heaved-in chain portion, the main wildcat being placed beyond said chain locker with respect to the direction in which the chain is heaved in by the main wildcat, an auxiliary wildcat disposed above the chain locker for engagement with an intermediate section of the chain which intermediate section extends between the main wildcat and the chain locker, and a torque motor drivingly connected to the auxiliary wildcat for imparting to said intermediate chain section a constant tension irrespective of the direction of rotation of the main wildcat.
 2. A device as claimed in claim 1, comprising a plurality of aligned chain lockers, a plurality of wildcats, each of which is located above a respective one of said plurality of chain lockers and drivingly connected to a corresponding torque motor for driving said auxiliary wildcat, the chain lockers being adapted to receive in succession a portion of said chain by the successive engagement of the chain with the associated auxiliary wildcat.
 3. A device as claimed in claim 2, wherein the main wildcat and the auxiliary wildcat have horizontal axes of rotation and are contained in the same vertical plane.
 4. A device as claimed in claim 2, comprising two main wildcats both driven by said main windlass, the aligned chain lockers being provided in two groups of chain lockers located respectively on the port side and starboard side of the vessel, the two main wildcats co-operating respectively with two auxiliary wildcats respectively pertaining to the two groups of chain lockers.
 5. A device as claimed in claim 1, comprising a single main wildcat having a vertical axis of rotation, a plurality of aligned chain lockers, the aligned chain lockers being provided in two groups of aligned chain lockers located respectively on the port side and starboard side of the vessel, a separate auxiliary wildcat having a horizontal axis of rotation being provided above each chain locker.
 6. A device as claimed in claim 1, comprising a single main wildcat having a vertical axis of rotation, a plurality of aligned chain lockers, the aligned chain lockers being provided in two groups of aligned chain lockers located respectively on the port side and starboard side of the vessel, and auxiliary wildcats which have vertical axes of rotation and are respectively associated with the two groups of aligned chain lockers.
 7. A device for heaving in, letting out and storing a chain, in particular on board a vessel such as a ship or a floating platform, comprising a main windlass provided with at least one main wildcat for engagement with the chain for heaving in and letting out the chain and connected to be driven by the windlass, a plurality of aligned chain lockers for receiving in succession heaved-in portions of said chain, the main wildcat being placed beyond said chain locKers with respect to the direction in which the chain is heaved in by the main wildcat, an auxiliary wildcat, a torque motor drivingly connected to the auxiliary wildcat, support means for carrying the assembly of said torque motor and said auxiliary wildcat and means associated with said support means for allowing translational movement of said support means above the chain lockers for engagement of said auxiliary wildcat with an intermediate section of the chain, which intermediate section extends between the main wildcat and that one of the chain lockers which is being filled with a portion of said chain by the auxiliary wildcat, said torque motor and said auxiliary wildcat imparting to said intermediate chain section a constant tension irrespective of the direction of rotation of the main wildcat.
 8. A device as claimed in claim 7, comprising two main wildcats both driven by said main windlass, the aligned chain lockers being provided in two groups of chain lockers located respectively on the port side and starboard side of the vessel, each main wildcat co-operating with a respective auxiliary wildcat, each auxiliary wildcat being drivingly connected to a torque motor whereby each auxiliary wildcat and each torque motor constitute an assembly mounted on a support means associated with a means allowing translational movement of said assembly above the respective group of aligned chain lockers.
 9. A device as claimed in claim 7, comprising a single main wildcat having a vertical axis of rotation, the aligned chain lockers being provided in two groups of aligned chain lockers located respectively on the port side and starboard side of the vessel, there being provided for each group of chain lockers an assembly of a torque motor and the corresponding auxiliary wildcat which has a horizontal axis of rotation, said assembly being mounted on a support means associated with means for allowing translational movement of said support means above the respective chain lockers, said assembly being pivotably mounted about a vertical axis on said support.
 10. A device as claimed in claim 9, further comprising, for each of said assemblies, rails extending on each side of the respective groups of chain lockers, a carriage for rolling along the rails, and a turret pivotably mounted on said carriage for supporting the corresponding assembly of a torque motor and an auxiliary wildcat.
 11. A device for heaving in, letting out and storing a chain, in particular on board a vessel such as a ship or a floating platform, comprising a main windlass provided with at least one main wildcat for engagement with the chain for heaving in and letting out the chain and connected to be driven by the windlass, a plurality of aligned chain lockers for receiving in succession heaved-in portions of said chain, the main wildcat being placed beyond said chain lockers with respect to the direction in which the chain is heaved in by the main wildcat, an auxiliary wildcat mounted to be movable in translation above the chain lockers for engagement with an intermediate section of the chain, which intermediate section extends between the main wildcat and that one of the chain lockers which is being filled with a portion of said chain by the auxiliary wildcat, and a torque motor drivingly connected to the auxiliary wildcat imparting to said intermediate chain section a constant tension irrespective of the direction of rotation of the main wildcat, said device further comprising rails extending on each side of the aligned chain lockers and a carriage for rolling along the rails, the auxiliary wildcat being mounted on the carriage.
 12. A device as claimed in claim 11, wherein the carriage is provided with drive means for shifting the carriage along the rails.
 13. A device as claimed in claim 11, wherein the carriage is combined with means for holding the carriage stationary in selected positions on the rails. 